Process for the isomerization of hydrocarbons

ABSTRACT

PARAFFINIC AND/OR ALKYL SUBSTITUTED AROMATIC HYDROCARBONS ARE ISOMERIZED WITH A CATALYST COMPRISING (A) A LEWIS ACID OF THE FORMULA MXN WHERE M IS SELECTED FROM GROUP IV-B, V OR VI-B OF THE PERIODIC TABLE, X IS A HALOGEN AND N VARIES FROM 3 TO 6, AND (B) A STRONG BRONSTED ACID COMPRISING FLUOROSULFURIC ACID, TRIFLUORO-   METHANESULFONIC ACID, TRIFLUOROACETIC ACID OR MIXTURES THEREOF.

Oct. 16, 1973 G. A. OLAH A PROCESS FOR THE ISOMERIZATION OF HYDROCARBONS Filed June 25, 1971 George A. 0/0!) INVENTOR mZON ZOEHMEMEOQ ATTORNEY United States Patent O 3,766,286 PROCESS FOR THE ISOMERIZATION F HYDROCARBONS George A. Olah, Cleveland, Ohio, assignor to Esso Research and Engineering Company Filed June 25, 1971, Ser. No. 156,822 Int. Cl. C07c /28 US. Cl. 260-668 A 17 Claims ABSTRACT OF THE DISCLOSURE Paraffinic and/or alkyl substituted aromatic hydrocarbons are isomerized with a catalyst comprising (a) a Lewis acid of the formula MX where M is selected from Group IV-B, V or VI-B of the Periodic Table, X is a halogen and n varies from 3 to 6, and (b) a strong Bronsted acid comprising fiuorosulfuric acid, trifluoromethanesulfonic acid, trifluoroacetic acid or mixtures thereof.

BACKGROUND OF THE INVENTION The present invention relates to a process for isomerizing paraffins and/or alkyl substituted aromatic hydrocarbons. More particularly, the invention relates to the isomerization of branched and straight chain aliphatic and cycloaliphatic hydrocarbons and/or alkyl substituted aromatic hydrocarbons at isomerization conditions in the presence of a strong acid catalyst. Still more particularly, the invention relates to the isomerization of C to C paraflins and alkyl substituted aromatic hydrocarbons in the presence of a catalyst comprising a Lewis acid and a strong Bronsted acid.

DESCRIPTION OF THE PRIOR ART It is well known that the more highly branched isomers of the paraffinic hydrocarbons occurring in petroleum oil gasoline fractions are more valuable than the corresponding slightly branched or straight chain hydrocarbons due to their higher octane ratings. The demand for gasolines with high octane numbers has been due chiefly to the production of gasoline engines with increasingly higher compression ratios. One of the economically important ways in which the increased demands for high octane fuels can be met is through the isomerization of light naphtha components of such fuels.

The isomerization of aliphatic, cycloaliphatic and alkyl aromatic hydrocarbons is well known. It is customary to employ certain Lewis acids, particularly aluminum chloride or aluminum bromide, in conjunction with certain promoters, such as hydrogen chloride, hydrogen bromide or hydrogen fluoride as isomerization catalysts. Thus, for example, Canadian Pats. 742,746 and 794,400 disclose the use of antimony pentafluoride/hydrogen fluoride in solution or on a solid support as an isomerization catalyst.

Insofar as the isomerization of light naphthas is concerned, the lower the temperature of isomerization, the more favorable is the equilibrium for converting straight chain paraffin hydrocarbons into branched chain isomers. One of the problems with the known catalyst systems is the relatively high temperatures that must be employed for the isomerization process. This may lead to increased cracking and disproportionation and, thus, a reduced yield of branched chain hydrocarbon. Another problem is the frequently high volatility of the catalyst system, necessitating pressurized reactor systems. It has now been found that these problems can be circumvented by use of the special acid catalyst systems of this invention.

SUMMARY OF THE INVENTION In accordance with this invention, isomerizable hydrocarbons selected from the group consisting of paraffin-s,

'ice

alkyl substituted aromatic hydrocarbons and mixtures thereof, containing, preferably, 4 to 20 carbon atoms per molecule are isomerized at low temperatures in the presence of a catalyst comprising (a) one or more Lewis acids of the formula MX where M is selected from Group IV-B, Group V or Group V'IB elements of the Periodic Table, X is a halogen, preferably fluorine, and n varies from 3 to 6, and (b) a strong Bronsted acid, preferably comprising a strong halogen-substituted acid such as fiuorosulfuric acid, trifluoromethanesulfonic acid, trifluoroacetic acid or mixtures thereof. The Periodic Table referred to is that described in The Encyclopedia of Chemistry, Reinhold Publishing Corporation, 2nd ed. (1966) at p. 790. The term elements as used herein refers to the metals and metalloids of the aforementioned groups of the Periodic Table.

Specific examples of useful Lewis acids include antimony pentafluoride, arsenic pentafluoride, tantalum pentafluoride, niobium pentafluoride, vanadium pentafluoride, titanium tetrafluoride, bismuth pentafluoride, phosphorus pentafluoride, molybdenum hexafluoride, zirconium tetrafiuoride, mixtures thereof and the like. Moreover, chlorine, bromine or iodine may be substituted for fluorine without affecting the efficiency of the catalyst system.

Preferably, the catalyst composition will comprise only one Lewis acid and one Bronsted acid. Exemplary of such catalyst compositions that are encompassed by this invention are the following.

Catalyst No.:

1 Antimony pentafluoride-fluorosulfuric acid. 2 Arsenic pentafluoride-fiuorosulfuric acid. 3 Tantalum pentafluoride-fluorosulfuric acid. 4 Niobium pentafluoride-fluorosulfuric acid. 5 Vanadium pentafiuoride-fluorosulfuric acid. 6 Titanium tetrafiuoride-fluorosulfuric acid. 7 Molybdenum hexafiuoride-fluorosulfuric acid. 8 Antimony pentafluoride-chlorosulfuric acid. 9 L Antimony pentafluoride-trifluoromethanesulfonic acid. 10 Arsenic pentafluoride-trifluoromethanesulfonic acid. 11 Tantalum pentafluoride-trifluoromethanesulfonic acid. 12 Niobium pentafluoride-trifluoromethanesulfonic acid. 13 Vanadium pentafluoride-trifluoromethanesulfonic acid. 14 Titanium tetrafluoride-trifluoromethanesulfonic acid. 15 Molybdenum hexafluoride-trifluoromethane-sulfonic acid. 16 Zirconium tetrafluoride-trifluoromethanesulfonic acid. 17 Antimony pentafluoride-trifluoroacetic acid. 18 Tantalum pentafluoride-trifluoroacetic acid. 19 Arsenic pentafluoride-trifluoroacetic acid. 20 Titanium tetrafluoride-trifluoroacetic acid. 21 Zirconium tetrafluoride-trifluoroacetic acid. 22 Vanadium pentafluoride-trifluoroacetic acid. 23 Molybdenum hexafluoride-trifluoroacetic acid. 24 Niobium pentafluoride-trifluoroacetic acid.

' termpresent ii'r the isomeriza ion -zone with jrefere the total amount'of hydrocarbo of; the catalyst composition per-part by Weightof.

, carbon. Preferablwthe' amount of catalyst present in I zone can rangejfrom '1 tolO'pa'rts; by weightoiithe ata; lysti compositioniper pareby weight'of; the'hy rocar n r volume ratio can'range. from about 550:1 to l": I' and erablyjfromflOcgltoZrl! f "in V j The icatalystjsystem? mayJbef 'employed incorporated with a suitable SQlid carrierorfsupport; AIlY fSQlldQCBl lyst support maybe used that iss'ubstantially inert. catalyst :underthe reactionfconditions;Thefsupportfshould p able solid supports include fluoride-treatedor coated res-ins I a 7 such assu-lfo'natejd cation exchange resins, fluoride rented r acidic chalcides such as alurnina; and aluminosilicate' and i rjasite The supp V able.manner such asfby coriventional methodsincludiug dry mixing cpprecipitation: or impregnationtiln on hating a suitablev deactivatedsupport with a meta fiuOn such asantimony pentafluoride and then with a Bronsted l acidsuch asifluorosulfuricacid. p V "The weight' ratio' ofxthe Lew s acid to the supper,

rangeifrom 12 100 to 1:10 and preferably, from 1:50 to i clude paraffiris, alkyl substituted-aromatic hydrocarbon v elude aliphatiof and cyclo alipha tic -1 hydrocar 'ons th substantially 'di 7 Th -a h lq 7 materials) can contain 4to locarbon atoms per rnolecule, preferably 4 to 8 carbon atoms, and. may be exemplified] The molar .raftio of Bronste i Lewis aci range from, about 2011' to 5 1 :Pr'eferably a 5: 1: t molar ratio islemployed. Theamountof, the cataly' r V U present'thereiri can from: about 0.01 to 100 parts; or ieven higherby The catalystmaybe used as the neat liquid; as a The catalyst, may be: used? as theizneat liquid,

acid, trifluoromethanesulfonici acid and, the' rlik e selves; can be "used asudiluents.,,The' diluentzcatalyst ret- 1 of: the invention, the hydrocarbonphasoand:catalyst phase may. be contacted suhStantiallygintheliquidyphase; The apparatus employedv may be of a conventional,nature and f may com prise a' single reactor sucl'rv asa fluid ized-bed be pretreated, suchlias ibyheating, chemical treatment or coating, towremoye substantially'all water and/or hy-Q I droxylic sites thatmight b'e.present.Active support may be renderedinert by coatingnthem' withfanwinertjmaterial such a's antimony trifluoride or aluminum trifiuoridefSu acid resisjtant olecular' sieves such as a zeolite'e ortejd catalysts can be'prepared in bodi-ment," the supported catalyst is prepared nvactifinrpressure can range from'about 1 atmosphere to 1:35. Thetweightratio ofthe'Bronsted-acid to thesiupport may'range fr to 1:35. .7 7 r i 7 Feedstocks that may be used in the instant process and mixtures thereof; The p 'airafitins' as :herein' 'deiin 'm 1:100 tol and prefei'ablutromil:QQ

by n-butane, n-pentane, methylpentane, methylhexane and the like. The ,cycloaliphatic hydrocarbons (naphthenes) can contain 6 to carbon atoms per molecule, preferably 6-12 carbon atoms, and may be exemplified by methylcyclopentane, the dimethylcyclopentanes, ethylcyclohexane, n-pentylcyclohexane and the like. Depending.

on reaction conditions, isomerization of the ring, i.e. ring expansion or contraction, may compete with side chainmatic hydrocarbons such as the xylenes, n-butyl benzene and the like. Both positional isomerizationof the alkyl groups substituted on the ring and side chain isomerization may occur depending on reactionconditions. Other aliphatic or alic'yclic hydrocarbons commonly found in conventional petroleum, hydrocarbon light naphtha '1 streams may also bepresent. k r r I L The feed may; contaiu'various cracking .inh'hitors or I moderators suchas hydrogen and the like s'fhe inhibitors during the isomerization, When hydroge is used,-; it" is employed, in; amounts ranging, preferab Y mole" percent based" on, hydrocarbon teed ,fimpurities such aswater; there rerthe. alikylatioushonld I be conductedsubstantially; 1n the ,abjsenceot large amounts of moisturaiie. by the useof arrhydrous'reagents, V by purificationof thelstartingreagents, e r p The process of 'th'e'in'yention isconduoe as;alratbltror continuous Ltype operatiom;In gene'rahrthewarious me ans customarily" employed extraction 7 processes ,ito

;; deyices, such as mechanical agitators-, jetsgo'f restricted I phase the catalystphasemay b passedthroug'hlone or more-reactors inconcurrentgj crosscurreutor counter-v and -heavier productsof the :reaction rnay be'separated r from thQ',d6Slfd isomeric produetand from oue another:

furtheriprocessedyas by alkylat'iontand the I ployed directly as a high octane. gasoline blen tugs-gene The reaction temperatures'for; the isomu i ationciau.

. atmospheres, The hydrocarboninediafibe in eitheuthfi I liquidor gaseous phase and'ispreferably predominantly l intheiiquid Phi 1 temperature and catalyst concentrations employed. In: gen- 1 and 10 hours,'usuaily 0; 2'to 5 hours, maybegemployeda will be, particularly described with, r

.. 1 pentafluorideltrifluoromethauesuitonie 1 acid catalyst sys tem' r t t- 4 r act'to depress excessive cleavage=reactions th mayoccur our lo to 3 The process catalyst system: is; somewhattsensitive to increase the contactarea between thehydrocarbon phase and the catalyst phase may be needs. In one} embodiment reactor or multiple reactors equipped-w efiicientfstirrin g internal diameter, turbo nrixers, etcg The hydrocarbon current flow. Unreasted reactant-g catalysts; inhibitors;

such as by distillation and returnedin whole or in part to the isomerization zone. Theresultantpr ductmaybe or be, em:

varyin the range of about toil'QO? 6;, us" g liquid catalystgand preferahly'ltlitogt) C1 whenausing sup ported solid acid catalysts, temperatures cau irangei-from ahout';+2'0toy350 C4, preferably. 5 0 toZOO CbThe re atmospheres and preferably'tronr' lYatmosp re toZE) '3 1 The contact time of the catalyst ,andhydrocarbon is subject to wide variation, beingfdepenrient inipart upon' tihe 5 r BRIEFDESCRIPTION" OF THE RAWI G 1 The" drawing is-a. flow-diagrams of a profsrr ed;etnbnodj.- mentRo-f the-invention; In thi'sco e "0' th efr at; not n-hemne in thegfpresen Referring now to the drawing in detail, n-hexane is p introduced into isomerizationzone 2, in the liquid phase, from a source, not shown, by way of line 1. An equimolar mixture of antimony pentafluoride and trifluoromethane sulfonic acid is introduced intoezone 2 via 1ine3, The amount of catalyst chargedlis. 20 g. per g. of n-hexane. The temperature within the isomerization zone is maintained between the range of 20 to 25 C. while the pressure is maintained at 1 atmosphere. The isomerization zone is provided with an agitator to ensure thorough contacting of the reactants. The contacting time I is. about 2-6 hours. 7

The .isomerized product is discharged from zone 2 via line 4 and sent to settling zone 5. Upon standing for a period of time, the product separates into a hydrocarbon phase and an inorganic phase containing the acid catalyst that is essentially insoluble. in the hydrocarbon phase. The separated acid catalyst is then withdrawn from zone 5 and recycled to the isomerization zone 2 via line 6 for reuse. The separated hydrocarbon phase is discharged from settling zone 5 via line 7 and contacted therein with caustic (e.g. about 20% by weight sodium hydroxide) introduced via line 8. The amount of caustic added thereto is gms. per 100 gms. of n-hexane. The n-hexane/caustic mixture is introduced into mixing zone 9 and intimate- 1y mixed therein. The mixture is then withdrawn from the mixing zone by means of line 10 and introduced into settling zone 11, wherein the caustic phase separates from the hydrocarbon phase.

The caustic phase is removed via line 12 and the hydrocarbon phase is removed via line 13 and introduced into a separation zone 14 illustrated as a distillation zone that is provided with a heating means such as steam coil 15 and with lines 16, 17, 18, 19 and 20. Conditions of temperature and pressure are adjusted in zone 14 to recover the product either in one fraction (line 16) or in several fractions by lines 17 and 18 While unreacted nhexane feed may be discharged by line 19 and preferably recycled to isomerization zone 2 via lines 19 and 1. The heavy side products are discharged from the separation Zone 14 by line 20.

The invention -Will be further understood by reference to the following examples that include a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Example 1 Several isomerization reactions were performed in a batchwise manner using a 500 cubic centimeter tetrafluoroethylene polymer (Tefion)-lined stainless-steel reactor, equipped with a stirring device. Normal hexane was used as the hydrocarbon feedstock. Reaction conditions and product distributions are given in the following table.

Product analysis Table I summarizes isomerization product compositions as determined by gas-liquid chromatography using a 150 foot, 0.01 inch I.D. squalene column and a hydrogen ionization flame detector.

'6 based isomerizations, thus minimizing complications arising from competitive side reactions.

What is claimed is:

1. A process for the isomerization of isomerizable hydrocarbons selected from the group consisting of paraffins, alkyl substituted aromatic hydrocarbons and mixtures thereof comprising contacting said isomerizable hydrocarbon at isomerization conditions with a catalyst comprising (a) a Lewis acid of the formula MX where M is selected from the Group V elements of the Periodic Table, X is a halogen and It varies from 3 to 6, and (b) a Bronsted acid comprising fluorosulfuric acid, said contacting occurring substantially in the liquid phase.

2. The process of claim 1 wherein said paraffins contain 4 to 20 carbon atoms per molecule and are selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons and where said alkyl substituted aromatic hydrocarbons contain 7 to 20 carbon atoms per molecule.

3. The process of claim 1 wherein the Lewis acid is selected from the group consisting of antimony pentafluoride, tantalum pentafluoride, niobium pentafluoride, vanadium pentafluoride, bismuth pentafiuoride, arsenic pentafluoride, and phosphorus pentafluoride.

4. The process of claim 1 wherein said catalyst consists of niobium pentafiuoride and fluorosulfuric acid.

5. The process of claim 1 wherein said catalyst consists of antimony pentafluoride and fluorosulfuric acid.

6. The process of claim 1 wherein said catalyst consists of tantalum pentafluoride and fiuorosulfuric acid.

7. The process of claim 1 wherein the catalyst and hydrocarbon are contacted in the presence of an inert diluent.

8. The process of claim 7 wherein said diluent is selected from the group consisting of sulfuryl chloride fluoride, sulfuryl fluoride and fiuorinated hydrocarbons.

9. A catalytic isomerization process comprising contacting isomerizable hydrocarbons selected from the group consisting of C to C paraffins, C to C alkyl substituted aromatic hydrocarbons and mixtures thereof, at isomerization conditions with a catalyst comprising (a) a metal fluoride wherein the metal is selected from the group consisting of titanium and Group V and Group TABLE I.-n-HEXANE ISOMERIZATION Run 1 Reaction conditions:

200 y CF3S03H-SbF5 Weight of catalyst, g. 33

Reaction time, h Reaction temperature, 0. Reaction pressure, atm

Percent (w./w.) catalyst/n-hexane Product analysis, wt. percent:

Butanes Isobutane..- n-Butane Pentanes 2:3-dirnethylbutane. 2-methylpentane 3-methylpentane--- Heptanes 2,2-dimethylpentane ZA-dimethylpentane 2,2,3-trimethylbutano 3,3-dimethylpentane 2-methylhexane 2,3-dimethylpentane 3-methylhexane 3-ethylpentane n-Heptane Methylcyelohexane Unidentified peaks Run 2 Run 3 Run 4 Run 6 Run 6 200 200 FSOaH-NbFa FSOaH-SbFB 3% 33 1 Catalyst consists of eqnimolar proportions of metal fluoride and Bronsted acid.

It will be noted from Table I that product of high C content can be prepared by use of the catalysts of this invention. Moreover, low reaction temperatures can VI-B metals of the Periodic Table, and (b) a Bronsted acid selected from the group consisting of fluorosulfuric acid, trifluoromethanesulfonic acid and trifluoroacetic be used to carry out the reactions vis-a-vis sulfuric acid acid wherein said contacting occurs substantially in the liquidphase and'at a temperature between about; ---30 I and-100 and at a pressurejhetween the range otjabout 1 atmosphere and 50 atmospheres. r V 10. The process of claim'9 wherein saidcatalystncomprises tantalum pentafluoride and fiuorosulfuric acid.-

"11. Arproce'ss for the isomerization roi isomerizable hydrocarbons selected from the group'consi'sting of paraf- I fins, alkyl substituted aromatic hydrocarbonsand mixtures thereofcomprising contacting said isomerizab lehy- 7 drocarbous .at isorneriz'ation' conditions with a catalyst comprising (a) a Lewis acid of theformula MX where M is selected from the group consisting of titanium, and

Table, X is a halogenrand n varies, from} to 6, and '(b) a Bronsted acid selected fromthe group consistingfljof trifluoromethanesulfonic"acid and trifluoroacetic acid;

7 H 12. Theprocess of claim 11 wherein saidicatalystconr t a sists of antimony pentafluoride and trifluorometh'anesulfonic acid. I a i a 13.-Tl1e process ofrclaim 11. wherein saidtcatalystrcon-fa sists "of tantalum pentafiuorid'e' and 'trifluoromethahesulP fonic acid. V V

4 Group V and Group: VI-B, elements of the Periodic r 14, The process of claim 11 wherein the catalystds supported on :a solid carrier that'issubstantially 'inert to-.2{5

the supported acid.

15. A process for the isomerization of an isomerizable a hydrocarbonselected from the group consisting of paraf- M is slected from the group consistingrof titaniur'nfand L Group V and Group 'YLB elements of v the Periodic Table, X is a halogen and 'n varies, from 3 to '6, andtb) fiuorosulfuric acid, where said fluorosulfuric acid and fins, alkyl :isubstituted: aromatic hydrocarbons and zmixa} tures thereof comprising contacting said" isomerizablefhyi drocarbons at isomerization conditions with'a catalyst comprising (a) a Lewis acid of the'formula MX' where? r Lewis acid are supported 'stautiaily inert. to said supported-"acids, siaid solidcarrier selected from the group consistingof fluoride-treated I, resins, fluoride-treated acidic chali d'es andacid-resistant gen and n' varies from 3 to 6, an'd: (blaBronsted on a solid carrier that 'is subrno'lecular sieves.

16'. A" process for the isomerizationof isomerizablc v hydrocarbons selected from the group consi sting'of paraffins,;alky1 substituted aromatichydrocarbons andmixtures thereof comprising contacting said isomezrizable by a idrocarbons at isomerization conditions "witha catalyst comprising (a) a Lewis acid of the formula MXg where o t M is selected from the group consisting of titanium and Group YI-B elements of the Periodic Table; X is a halocom-prising fluorosulfuric acid V 17. In a process for the isomerization of an isomeriz- V able hydrocarbon selected from thegroup copsistiug' of 'paraffins, alkyl substituted aromatic hydrocarbons and i mixtures thereof, the step. of contacting said isomeriz-able hydrocarbon at isomerizationconditions with a catalyst I comprlsing vantimony pentafiuoride and ,trifluotoacetic' CURTIS R. DAVIS, Primary Examiner Y- U.S. 01. x3.

acid 

